In a general wireless communication system, only a single carrier may be considered even though bandwidths between an uplink and a downlink are set up to be different from each other. For example, on the basis of a single carrier, a wireless communication system may be provided, in which the number of carriers constituting the uplink and the number of carriers constituting the downlink may be 1, respectively, and a bandwidth of the uplink is symmetrical to that of the downlink.
In the International Telecommunication Union (ITU), it is required that the candidate technology of the IMT-Advanced should support an extended bandwidth as compared with a wireless communication system according to the related art. However, except for some areas of the world, it is difficult to allocate frequencies of wide bandwidths. Therefore, as a technique for effectively using fragmented small bands, a carrier aggregation (bandwidth aggregation or spectrum aggregation) technique is being developed to obtain the same effect as when a band of a logically wide bandwidth is used by physically aggregating a plurality of bands in a frequency domain.
The carrier aggregation is introduced to support increased throughput, prevent the cost from being increased by a wideband RF device, and ensure compatibility with the existing system. The carrier aggregation refers to a technique of enabling data exchange between a user equipment and a base station through a plurality of groups of carriers of a bandwidth unit defined in the existing wireless communication system (LTE system in case of the LTE-A system, and IEEE 802.16e system in case of the IEEE 802.16m system). In this case, the carriers of a bandwidth unit defined in the existing wireless communication system may be referred to as component carriers (CC). For example, the carrier aggregation technique may include a technique for supporting a system bandwidth of 100 MHz by using maximum five component carriers even if one component carrier supports a bandwidth of 5 MHz, 10 MHz or 20 MHz.
If the carrier aggregation technique is used, data may be transmitted and received through several uplink/downlink component carriers. Accordingly, the user equipment may monitor and measure all the component carriers. If data are transmitted and received on all the component carriers, there is no problem. However, the user equipment performs monitoring and measurement operations for a component carrier on which data are not transmitted and received, whereby unnecessary power consumption (battery consumption) of the user equipment may be caused.